The present invention relates to a mixing and application capsule for producing a dental preparation.
Mixing and application capsules allow a mixing of solid and fluid components in order, for example, to produce a dental preparation, which is then applied from the mixing and application capsule in the oral cavity of the patient. In order to produce glass ionomer cement, for example, a powder component is mixed with a liquid component. Various methods are known in the prior art to accommodate the liquid which is mixed on activation of the mixing and application capsule with the powdery component in order to produce the dental preparation.
The liquid is accommodated, for example, in a foil pouch, which is opened by bursting. The foil pouch is then squeezed out in order to press the liquid out of it and feed it to the powdery component. This method has the disadvantage that with a pouch which is very long in relation to the pouch diameter, in particular, the foil produces folds when being squeezed together, in which an indeterminate liquid residue remains. The result is that the dental preparation compound is mixed with too little fluid, so it does not have the desired properties. Therefore, either the size of the foil pouch and thus the liquid quantity are limited or else the dosage is imprecise. The diameter of the foil pouch cannot generally be varied as desired as the capsule would have to have a correspondingly larger diameter. A capsule with a larger diameter is, however, disadvantageous on application in the oral cavity of a patient. Also, the squeezing-out tongs used when squeezing out the mixing and application capsule are generally adapted for small capsule diameters.
A variation is that a foil pouch is arranged laterally on or at the capsule body. A pouch of this type may therefore have a significantly larger diameter and liquid quantity. However, the disadvantage exists that a separate activation tool is necessary to open the foil pouch and to bring its content in the capsule in contact with the powder (i.e. to activate the capsule). Also, proportionally more liquid remains in a pouch with a large diameter.
A further example of accommodating a liquid in a mixing and application capsule for producing a dental preparation is described in U.S. Pat. No. 6,386,872 B1. Arranged in the interior of the capsule body are a first and a second plunger, in the intermediate space of which a liquid is arranged. The first plunger delimits the mixing chamber in the interior of the plunger body, in which the powdery component is arranged. The plunger wall between the mixing chamber and liquid chamber has a desired breaking point. If the second plunger is pushed in the direction of the mixing chamber, a projection of the second plunger breaks through the desired breaking point of the wall of the first plunger, so the liquid flows into the mixing chamber in order to be mixed there with the powdery component. After the activation, for example in that the capsule is pressed by hand onto a table surface, the capsule has to be clamped into a mixing apparatus, which mixes the powder and liquid to form a paste by means of shaking movements.
The capsule is then clamped in squeezing-out tongs, with the aid of which the two plungers are moved further forward. The paste is discharged in the process through the cannula and, for example, used to fill a cavity of a tooth to be treated.
The arrangement according to U.S. Pat. No. 6,386,872 B1 has the disadvantage that diffusion losses of the liquid exist and the mixing and application capsule is therefore not suitable to be stored over a relatively long time period. The seal between the first and the second plunger is a sliding seal. If the seal is selected to be smooth-running, so a displacement of the second plunger relative to the first plunger is possible manually, there is an insufficient seal and the liquid can evaporate between the first and second plunger. If the seal is selected to be so tight that evaporation of the liquid through the seal is virtually completely avoided, the second plunger can only be displaced relative to the first plunger with the application of a large force which requires special tools and is no longer possible manually. Furthermore, a similar problem of liquid evaporation exists for the seal between the first plunger and the capsule body. The powdery component in the mixing chamber is hygroscopic and therefore tends to absorb moisture entering through the seal between the first plunger and capsule body. This also impairs the long-term storability of the mixing and application capsule. In addition, the thin-walled desired breaking point region of the wall of the first plunger is easy for the liquid to penetrate. The powdery component can therefore not only absorb moisture from the liquid via the seal between the first plunger and capsule body, but also through the desired breaking point region of the wall of the first plunger.
Further examples, also with a sliding seal are to be found, for example, in EP 1 226 790 or also in JP 2001340356.
WO 03/028871 A1 discloses a mixing capsule for a two-component mixing with a cylindrical container part and a spray nozzle molded onto the end face. A plunger is axially displaceably guided in the container part. Provided in the end face of the plunger is an opening adjoined by a liquid receptacle with a burstable wall or membrane. When the capsule is not activated, the membrane seals the opening. The cavity between the end faces of the container part and the plunger forms a mixing chamber. A movable activating part is provided in the mixing chamber. The activating part can be displaced by means of an activating pin sealing the spray nozzle in the non-activated state. In the activated state of the capsule, the activating part is substantially completely received in the liquid receptacle.